Surgical procedures necessarily involve the transection of vessels as surgeons seek to explore, remove, or repair tissue defined systems. Transection is carried out with a variety of cutting instruments ranging from a cold scalpel to electrosurgical devices. As such vessels are cut, it generally is necessary to accommodate bleeding by microsurgical or similar approaches, or where smaller vessels are encountered, by a sealing and congealing procedure. This latter procedure typically is carried out by heating the involved tissue and fluids through the application of electrical current at RF frequencies developed by an electrosurgical generator. Effective sealing of smaller vessels is important to surgical procedures, inasmuch as even a small blood flow not only can obscure the surgeon's field of view, but also may accumulate with the risk of hematoma or significant blood loss.
While a variety of electrosurgical instruments have been developed to achieve hemostasis, many are of marginal effectiveness for certain surgical tasks, particularly those involving small vessels and small, highly localized tissue regions of interest. To carry out such somewhat delicate surgical procedures requisite to such regions, practitioners typically employ forceps, instruments of common utility which, in effect, represent a thin extension of the thumb and forefinger function of the surgeon. Forceps generally serve to provide a tissue or vessel grasping function, having working ends or tip portions which may be of diminutive dimension enabling the surgeon to locate and grasp small vessels which have a tendency to retract into tissue following their being cut. By applying bipolar, RF current from a noted electrosurgical generator across the outer working end tips of the forceps, a sealing or congealing of tissue or vessels can be achieved without substantial risk to adjacent tissue. In effect, the well defined tips of the bipolar forceps provide a more precise attainment of hemostasis.
Another surgical application for bipolar forceps has been referred to as "coagulative painting" where typically, the side surfaces of the electrically active tip regions of the forceps' tines are drawn over the surface of membranous tissue such as the mesentery. Done properly, this action congeals the small, microvessels within such thin tissues.
Electrosurgically driven forceps heretofore made available to surgeons, however, have exhibited operational drawbacks, which, in turn, have compromised their surgical effectiveness. To effectively carry out hemostasis, the electrically operative tips of the forceps should efficiently conduct a proper current flow through the tissue grasped. When that current is insufficient, coagulation of the tissue or vessel is compromised. When the current is excessive, correspondingly excessive heating occurs with a potential for the generation of damaging electrical arcing. Excessive heating also results in the phenomenon of tissue and blood coagulum sticking to the surface of the instrument. This results in the development of a layer of increased electrical impedance between the electrodes of the instrument and that tissue which may subsequently be grasped for the purpose of treatment. Additionally, such sticking tissue evokes a disruption of the coagulated surface which, in itself, may compromise the intended hemostatic effect. Consequently, bipolar forceps designs have been seen to incorporate highly polished electrode surfaces for the purpose of reducing the extent of tissue sticking as well as to facilitate their cleaning when sticking does occur. Unfortunately, when such modification of the forceps is carried out, the original grasping function of the forceps is substantially compromised.
Another problem encountered with the use of bipolar forceps of conventional design has been associated with their use in conjunction with thin tissue. As such tissue is grasped between the opposed bipolar electrodes of the instruments, only a low tissue related impedance is witnessed by the electrosurgical generator associated with the instrument, which conventionally reacts to decrease its output toward zero as tissue impedance approaches a zero value.
Use of the bipolar forceps also becomes problematic in conjunction with the noted "coagulative painting" procedure where the side surfaces of the instrument are drawn across the surface of membranous tissue. The electrical model involved in this procedure is one wherein current is caused to flow from the side surface of one tine, thence across a thin layer of tissue to the oppositely disposed spaced apart electrically operant tine. This calls for maintenance of the spacing between the two tines to avoid short circuiting the system and for a control over what is, in effect, a moving line source of heat applied to the affected tissue. Very often, a misjudgment may lead to the tearing of tissue in the procedure. Of course, it also is necessary for the surgeon to maintain a spacing between tine electrodes of the instrument to achieve requisite performance.
Approaches to minimizing the phenomenon of tissue sticking to the operative tips of bipolar forceps have been advanced by the medical instrument industry. For example, designs have propounded the use of forceps' legs having cross-sectional areas and which exhibit conductivity sufficiently high to maintain electrically operative portions for the instruments below threshold temperatures considered to evoke tissue sticking. Similarly, the temperature of the grasping tips of the forceps has been reduced by enlarging the cross-sectional radii of the forceps sufficiently to maintain current density and resultant tissue heating below the threshold temperature evoking sticking. See in this regard, U.S. Pat. Nos. 3,685,518; 4,492,231; and 5,196,009. However, the election of a large cross-sectional area at the grasping tips of the forceps for purposes of heat conduction compromises the basically sought precision of the forceps type instrument with respect to grasping and localized coagulation of smaller blood vessels, e.g. vessels smaller than about 1 mm in diameter.
An approach to limiting the heating of the tissue or vessel being coagulated with bipolar forceps has been to utilize a layer of a ceramic material having a thermal conductivity much lower than that of the metal used in the structure of the forceps. U.S. Pat. No. 5,151,102 describes such an arrangement wherein a plurality of silver filled epoxy electrodes are embedded within the ceramic coatings. However, Joulean heating with bipolar systems occurs within the tissue which, for such arrangements, has no effective pathway through which to dissipate, resulting in an enhancement of the sticking problem which now occurs at the ceramic layer.
To regain the originally desired grasping feature of forceps, the utilization of a roughened or tooth-like surface in conjunction with the electrically operative ends of the forceps has been proposed as represented in U.S. Pat. Nos. 5,330,471 and 5,391,166. By disposing a layer of insulation on the teeth of one or both of the grasping surfaces, electrical current only passes along the sides of the electrode surfaces which are outwardly disposed from the grasping surfaces. Thus, the utility of the forceps is compromised to the extent that only thicker tissues can be grasped and coagulated efficiently. In general, serrated or multi-pyramidally configured grasping surfaces prove difficult to clean during surgery due to the recesses and grooves which tend to trap tissue debris and coagulum.
U.S. Pat. No. 5,403,312 describes a combination of an electrosurgical forceps form of instrument which additionally carries out a stapling function. Intended for the grasping of thicker tissue components, the device described employs operative forceps tips with mutually offset or staggered electrode regions suitable for more extended thickness' of tissue as opposed to thin tissue. By mounting the electrode regions within a plastic support member, an otherwise desired feature for heat removal is compromised permitting the electrodes to reach temperatures during tissue coagulation that can exceed sticking threshold temperatures with the noted undesirable cleaning requirements.
Some investigators have proposed the utilization of temperature sensors such as thermocouples which are incorporated within the bipolar forceps instruments. Propounded in U.S. Pat. Nos. 5,443,463; 4,938,761; and 5,540,684, the approach requires that a special control system be provided which precludes the utilization of the ubiquitous conventional electrosurgical generator currently available in operating theaters throughout the world. Further, the otherwise simple construction of the forceps must be abandoned to a less desirable, highly complex instrumentation with such an approach.